Myllokunmingia may be one of the earliest known creatures with a backbone, and this creature may have possessed a rudimentary cameralike eye, which suggests vision dates back at least 520 million years. However, much remains unknown about the evolution of vision, since the soft tissue of the eye usually decays rapidly after death. To learn more about the evolution of vision, scientists analyzed an exceptionally well-preserved 300-million-year-old fossil specimen of a fish called Acanthodes bridgei. The fossil was excavated from Kansas and is kept at the National Museum of Nature and Science in Tokyo. The fish, which reached up to about 4 inches (10 centimeters) long, is the last known common ancestor of modern jawed fishes, including fishes with bony skeletons, such as barracudas, and cartilage skeletons, such as sharks. The researchers discovered the first record of fossilized rod cells and cone cells in this fish. Rods and cones are not usually preserved, because these soft tissues are more fragile, said lead study author Gengo Tanaka, a paleontologist at Kumamoto University in Japan. The scientists also found granules in the fossil that, based on the similarity of their chemistry, size and shape to particles found in modern fish eyes, are made of eumelanin, a pigment that absorbs light and helps animals see. A. bridgei is thought to have lived in shallow waters, through which most of the colors visible to humans from sunlight may have been also visible to the fish. As such, color vision could have proved invaluable for the fish — for instance, helping it spot predators and food.
Posted on: Tue, 23 Dec 2014 21:53:36 +0000
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